The influence of vegetation on rain garden hydrological performance

Rain gardens are increasingly adopted in urban areas to mitigate urban stormwater impacts. They provide an opportunity to adopt taxonomically diverse plantings to enhance habitat and aesthetic value. However, few studies to date have quantified how rain garden hydrological performance is affected by vegetation type. In the present study, two vegetation types were considered: taxonomically diverse communities composed of forb-rich perennials; and mown grasses, as well as a bare soil control group. Detention effects were measured independently from retention. The forb-rich perennial mixes consistently provided the best hydrologic performance in terms of both stormwater retention and detention. The diverse perennial community showed up to 1.2 mm higher initial losses over the experimental catchment compared with mown grasses, and also offered 54 and 32% longer detention compared with bare soils and mown grasses respectively. We therefore recommend prioritising taxonomically and structurally diverse planting for vegetated stormwater management facilities wherever possible.